Only desktop wallpaper after login F15

[Freak Trick]

Yesterday, I installed F15 from Live CD (downloaded around May release of the version). The first run was fine and I was able to install all usual applications - Chrome, Audacious, VLC, gcc, gcc-c++. Next morning, when I started the machine, I could reach up to the login menu and login successfully, thereafter the screen only had the default F15/Gnome3 wallpaper and the mouse cursor; nothing else would appear. Not even the task bar. Only keys which were being responded to where Ctrl+Alt+Del giving a logout dialog.

I formatted and reinstalled. Again it worked fine the first time. But next boot gave the same problem. Moreover without being able to access the desktop, I am short of ideas to do anything to resolve the problem.

Any workarounds?
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